A write-back and/or write caching technique may be a data transfer method in which an acknowledgement is sent to a host server from a disk array controller when data arrives from the host server to the controller's cache memory. This data may be referred to as “dirty data” till the point when it is written to the data store (e.g., the backend disks).
The dirty data may be an information arriving from the host server to the cache memory prior to transport to a data store. For example, the dirty data may be the information which has arrived from the host server to the cache memory on the controller but has not been written to the data store. The dirty data may be also referred to as “unwritten” data as far as the controller is concerned and is stored in units of cache blocks within the controller cache memory. At the time of a power outage, the dirty data in the cache memory may not be transferred to the data store and may be lost.